Continuity mistake: When Michael Keaton is talking to his wife he picks up Froot Loops, then a second later he picks up Cheerios.
Continuity mistake: When the original Doug brings the concrete worker to fix the house for Laura, Keaton uses a red sweater with a number one on it, and a white t-shirt under; But a couple scenes later, when he is talking to number three Doug and eating a sandwich, the white t-shirt has disappeared.
Continuity mistake: When Doug is in the boat and sits up and starts talking about his life, he sits upright against the cushion, but after he says "I wasn't in it", he's leaning back.
Continuity mistake: When Doug 2 wakes up, his head is either above the pillow or below, depending on the shot.
